KR20240021276A - Winding iron core and manufacturing method of the winding iron core - Google Patents

Abstract

A winding iron core with excellent magnetic properties and small transformer core loss is provided without using two or more types of materials with different magnetic properties.
The winding iron core of the present invention is made of a grain-oriented electrical steel sheet, has a flat portion and a corner portion adjacent to the flat portion, has a wrap portion on the flat portion, has a bent portion on the corner portion, and has a shape viewed from the side. The ratio of the length of the outer circumference to the length of the inner circumference (outer circumference length/inner circumference length) is 1.80 or less, and the magnetic flux density B8 of the grain-oriented electrical steel sheet when the magnetic field strength H is 800 A/m is 1.84 T or more. It is 1.91 T or less, and the iron loss deterioration rate under a predetermined compressive stress is 1.50 or less.

Description

Winding iron core and manufacturing method of the winding iron core

The present invention relates to a winding iron core and a method of manufacturing a winding iron core, and in particular, to a method of manufacturing a winding iron core and a winding iron core of a transformer, which are manufactured using grain-oriented electrical steel sheets.

A grain-oriented electrical steel sheet having a crystal structure in which the <001> orientation, which is the easy axis of magnetization of iron, is highly aligned with the rolling direction of the steel sheet, is particularly used as an iron core material for power transformers. Transformers, based on their iron core structure, are broadly divided into red core transformers and coiled core transformers. A red core transformer is one that forms an iron core by stacking steel plates cut into a predetermined shape. On the other hand, a wound iron core transformer forms an iron core by winding steel plates over and over again. There are many things required for a transformer iron core, but what is especially important is small iron loss.

From that point of view, it is important that the iron loss is small as a characteristic required for grain-oriented electrical steel sheets, which are the material of the iron core. Additionally, in order to reduce copper loss by reducing the excitation current in the transformer, it is necessary to have a high magnetic flux density. This magnetic flux density is evaluated as the magnetic flux density B8 (T) when the magnetizing force is 800 A/m, and generally, the higher the orientation integration in the Goss orientation, the larger B8 becomes. Electrical steel sheets with high magnetic flux density generally have small hysteresis loss and are excellent in iron loss characteristics. In addition, in order to reduce iron loss, it becomes important to adjust the crystal orientation of the secondary recrystallized grains in the steel sheet to a high Goss orientation and to reduce impurities in the steel components.

However, since there are limitations in controlling the crystal orientation and reducing impurities, a technology to reduce iron loss by introducing non-uniformity to the surface of the steel sheet through physical methods and refining the width of the magnetic domain, that is, magnetic domain refinement technology, has been developed. there is. For example, Patent Document 1 and Patent Document 2 describe a heat-resistant magnetic domain refining method for forming linear grooves of a predetermined depth on the surface of a steel plate. Patent Document 1 above describes a means for forming grooves using a gear-type roll. Additionally, Patent Document 2 describes a means for forming linear grooves on the surface of a steel sheet by etching treatment. These means have the advantage that the magnetic domain refinement effect applied to the steel sheet is not lost even when heat treatment, such as strain removal annealing, is performed during the formation of the rolled iron core, and that it can be applied to the rolled iron core, etc.

In order to reduce the core loss of a transformer, it is generally thought that the core loss (material core loss) of the grain-oriented electrical steel sheet, which is the iron core material, should be reduced. On the other hand, compared to the material core loss, the core loss in the transformer often increases. The value obtained by dividing the core loss value (transformer core loss) when an electrical steel sheet is used as the iron core of a transformer by the core loss value of the material obtained in the Epstein test, etc. is generally called the building factor (BF) or destruction factor (DF). In short, in transformers, BF generally exceeds 1. If BF can be reduced, transformer iron loss can be reduced.

As a general knowledge, the factor (BF factor) that causes the transformer iron loss in a wound iron core transformer to increase compared to the material iron loss is the magnetic flux concentration inside the iron core caused by the difference in magnetic field, and the steel plate joint. The occurrence of in-plane eddy current loss and an increase in core loss due to introduction of strain during processing have been pointed out.

Describes the increase in iron loss due to concentration of magnetic flux inside the iron core caused by differences in magnetic field. In the case of the single-phase winding iron core shown in FIG. 1, the magnetic path (inner magnetic path) on the inside (inner circumference side) of the iron core is shorter than the magnetic path (outer magnetic path) on the outer side (outer circumference) of the iron core, so the magnetic flux is concentrated inside the iron core. In general, the iron loss of a magnetic material rapidly increases non-linearly as the excitation magnetic flux density approaches saturation magnetization. Therefore, when the magnetic flux is concentrated inside the iron core, the iron loss inside the iron core increases unusually, and as a result, the iron loss of the entire iron core increases.

The occurrence of in-plane eddy current loss in steel plate joints is described. Generally, in a winding core for a transformer, a cut portion is formed to insert the winding. After the winding is inserted into the iron core from the cut portion, the steel sheets are joined to each other by forming a wrap portion. As shown in FIG. 2, in a steel plate joint, an in-plane eddy current is generated because magnetic flux moves in the perpendicular direction from the wrapped portion (wrap portion) to the adjacent steel plate. For this reason, iron loss increases locally.

The introduction of strain during processing also becomes a factor in increasing iron loss. If strain is introduced by slits in the steel sheet, bending during iron core processing, etc., the magnetic properties of the steel sheet deteriorate and the transformer iron loss increases. In the case of a rolled iron core, so-called strain relief annealing, which is annealing at a temperature higher than the temperature at which strain is released after processing the iron core, is generally performed.

Based on these factors for increasing transformer iron loss, the following proposals have been made, for example, as measures to reduce transformer iron loss.

In Patent Document 3, an electrical steel sheet with inferior magnetic properties compared to the outer circumferential side of the iron core with a short magnetic field is placed on the inner circumferential side of the iron core, and an electrical steel sheet with superior magnetic properties than the inner circumferential side of the iron core is placed on the outer circumferential side of the iron core with a long magnetic field, thereby increasing the magnetic flux to the inner circumferential side of the iron core. It is disclosed that by avoiding the concentration of the transformer core loss is effectively reduced. Patent Document 4 discloses an iron core design method that reduces transformer core loss by controlling the concentration of magnetic flux and the resulting core loss deterioration by combining multiple types of electrical steel sheets with different magnetic permeability and core loss.

Japanese Patent Publication No. 62-53579 Japanese Patent Publication No. 2895670 Japanese Patent Publication No. 5286292 Japanese Patent Publication No. 2006-185999

As disclosed in Patent Documents 3 and 4, transformer characteristics can be efficiently improved by using different materials on the inner and outer sides of the iron core to avoid concentration of magnetic flux on the inner side of the iron core. However, these methods require the appropriate arrangement of two types of materials (materials) with different magnetic properties (core loss), which makes transformer design complicated and significantly reduces manufacturability.

The purpose of the present invention is to provide a winding iron core with excellent magnetic properties and low transformer core loss, and a method for manufacturing the same, without using two or more types of materials with different magnetic properties.

In order to obtain a winding iron core with excellent magnetic properties and small core loss in a transformer, it is necessary to design an iron core that reduces the concentration of magnetic flux and select an iron core material that can suppress the increase in iron loss even if the magnetic flux is concentrated inside the iron core.

The following three points are required for iron core design to alleviate the concentration of magnetic flux.

(1) A winding iron core having a flat portion and a corner portion adjacent to the flat portion, a wrap portion on the flat portion, and a bent portion on the corner portion.

(2) As the iron core material, use a grain-oriented electrical steel sheet with a magnetic flux density B8 of 1.91 T or less when the magnetic field intensity H is 800 A/m.

(3) The ratio of the length of the outer circumference of the iron core to the length of the inner circumference (outer circumference length/inner circumference length) is 1.80 or less.

In addition, the following points are necessary for selecting an iron core material that can suppress the increase in iron loss even if the magnetic flux is concentrated inside the iron core.

(4) Using a grain-oriented electrical steel sheet with a magnetic flux density B8 of 1.84 T or more when the magnetic field intensity H is 800 A/m.

(5) Use a grain-oriented electrical steel sheet with an iron loss deterioration rate under compressive stress calculated by the formula below of 1.50 or less.

Core loss deterioration rate under compressive stress = (core loss at 5 MPa compressive stress)/(core loss in the absence of compressive stress)

Here, the iron loss at a compressive stress of 5 MPa and the iron loss in the absence of compressive stress in the above equation are the iron loss (W/kg) measured under the conditions of a frequency of 50 Hz and a maximum magnetization of 1.7 T, respectively, and the compressive stress The iron loss at 5 MPa is the iron loss measured at a compressive stress of 5 MPa in the rolling direction of the iron core material.

Each requirement and reason are explained in detail.

(1) A winding iron core having a flat portion and a corner portion adjacent to the flat portion, a wrap portion on the flat portion, and a bent portion on the corner portion.

The wound iron core is made by winding a magnetic material such as a grain-oriented electrical steel sheet to form a core. In general, a method is taken to wind a steel sheet into a cylindrical shape, then press the corner portions to a certain curvature and form them into a rectangular shape. On the other hand, as another manufacturing method, there is a method of making a rolled iron core by bending the corner part of the rolled iron core in advance and overlapping the bent steel sheets. The iron core formed by this method has bent portions (bent portions) at the corners. The iron core formed by the former method is commonly called tranco-core, and the iron core formed by the latter method is commonly called unicore or duocore depending on the number of steel plate joints formed. In order to alleviate the concentration of magnetic flux, a structure in which a bent portion (bending portion) is formed in the corner portion formed by the latter method is suitable.

The following experimental results show the results of an experimental investigation into the concentration of magnetic flux in the iron cores of tranco cores and uni cores. An iron core of one tranco core and two unicores of the shape shown in FIG. 3 is formed by winding a 0.23 mm thick grain-oriented electrical steel sheet (magnetic flux density B8: 1.89 T, W17/50: 0.86 W/kg), Strain removal annealing was performed on one tranco core and one unico core under the same conditions. For the production of the core, 50 turns of winding were performed, and no-load excitation was performed at a magnetic flux density of 1.5 T and a frequency of 60 Hz. A single-turn search coil was placed at the position shown in Fig. 4, and the magnetic flux density distribution within the iron core was investigated. Figure 5 shows the maximum value of the magnetic flux density of each 1/4-thick iron core from the inner (inner) to the outer (outer) windings. It can be seen that for both tranco cores (with strain relief annealing) and unicores (with strain relief annealing and without strain relief annealing), the magnetic flux density is greater in the inner coil, and concentration of magnetic flux occurs. When comparing tranco cores and unicores, it was found that unicores had a smaller concentration of magnetic flux.

The reason why the concentration of magnetic flux is alleviated by forming a uni-core, that is, a bent portion at the corner, is estimated as follows. Even if strain removal annealing is performed on the bent portion of the unicore, strain twins and the like remain, and the magnetic permeability is locally reduced compared to other portions. If such a portion exists where the permeability is significantly small, magnetic flux above a certain level cannot pass through. Therefore, even if there is a magnetic field difference, it is difficult for the magnetic flux to concentrate only inside the iron core. That is, it is estimated that in the inner winding part of the unicore, concentration of magnetic flux does not occur compared to the tranco core that does not have a bending part with a small magnetic permeability.

(2) As the iron core material, use a grain-oriented electrical steel sheet with a magnetic flux density B8 of 1.91 T or less when the magnetic field intensity H is 800 A/m.

The results of experimentally investigating the effect of magnetic flux density B8 on the magnetic flux concentration within the iron core of the unicore are shown. A single-phase unicore of the shape shown in FIG. 3 was produced from grain-oriented electrical steel sheets with a thickness of 0.23 mm and different magnetic flux densities B8 shown in Table 1. 50 turns of winding were performed, and no-load excitation was performed at a magnetic flux density of 1.5 T and a frequency of 60 Hz. A single-turn search coil was placed at the position shown in Fig. 4, and the magnetic flux density distribution within the iron core was investigated. Fig. 6 shows the maximum value of the magnetic flux density of each 1/4 thickness of the iron core from the inner to the outer circle in a uni-core made of each material (grain-oriented electrical steel sheet). As a result, the smaller the magnetic flux density B8 of the grain-oriented electrical steel sheet, the lower the concentration of magnetic flux, but at 1.91 T or less, this tendency was saturated.

The reason why the concentration of magnetic flux when used as an iron core is reduced as the magnetic flux density B8 of the grain-oriented electrical steel sheet as a material decreases is estimated as follows. If the magnetic flux density B8 of the iron core material is large, a large amount of magnetic flux can generally pass through. It is thought that when the magnetic flux density B8 of the iron core material is large, magnetic flux concentration inside the iron core is likely to occur due to the magnetic field difference. Conversely, if the magnetic flux density B8 of the iron core material is small, the magnetic flux can only pass to a certain extent. Therefore, even if there is a magnetic field difference, it is difficult for the magnetic flux to concentrate only inside the iron core. In other words, it is assumed that when the magnetic flux density B8 of the iron core material is small, the concentration of the magnetic flux in the iron core is relaxed compared to the case where the magnetic flux density B8 is large.

(3) The ratio of the length of the outer circumference of the iron core to the length of the inner circumference (outer circumference length/inner circumference length) is 1.80 or less.

The results of an experimental investigation of the effect of the magnetic field difference between the inside and outside of the iron core on magnetic flux concentration are presented. In the shape shown in Figure 7 and Table 2, the iron core was manufactured with a 0.23 mm thick grain-oriented electrical steel sheet (magnetic flux density B8: 1.89 T, W17/50: 0.86 W/kg) with the length ratio of the inner and outer circumferences of the iron core changed. did. 50 turns of winding were performed, and no-load excitation was performed at a magnetic flux density of 1.5 T and a frequency of 60 Hz. A single-turn search coil was placed at the position shown in Fig. 4, and the magnetic flux density distribution within the iron core was investigated. Although the magnetic flux density is increasing from the outer to the inner circle, the difference in magnetic flux density between the innermost circle position (position (i)) and the outermost circle position (position (iv)) is defined as the concentration of the magnetic flux to the inner side. Figure 8 shows the relationship between the ratio of the length of the outer circumference to the length of the inner circumference (outer circumference length/inner circumference length) for each iron core shape and the concentration of magnetic flux inside the iron core. As the ratio of the length of the outer circumference to the length of the inner circumference becomes smaller, the magnetic field difference between the inside and the outside of the iron core becomes smaller, so the concentration of magnetic flux inside the iron core becomes smaller. In particular, when the ratio of the length of the outer circumference to the length of the inner circumference was 1.80 or less, the concentration of magnetic flux inside the iron core was small.

Additionally, in Table 2, the length of the inner periphery was calculated as 2(c+d)+4f×(√2-2). Additionally, the length of the outer circumference was calculated as 2(a+b)+4e×(√2-2). Additionally, a and b were calculated as a = c + 2w and b = d + 2w, respectively.

In addition, the inner circumference length and the outer circumference length may be calculated from the lengths of each location as shown in Table 2, or the inner circumference length and the outer circumference length may be measured respectively.

Next, the conditions and reasons for selecting an iron core material that suppresses the increase in iron loss when the magnetic flux is concentrated inside the iron core will be explained.

(4) Using a grain-oriented electrical steel sheet with a magnetic flux density B8 of 1.84 T or more when the magnetic field intensity H is 800 A/m.

In general, the iron loss of a magnetic material rapidly increases non-linearly as the excitation magnetic flux density approaches saturation magnetization. Therefore, as described above, when the magnetic flux is concentrated inside the iron core and the local magnetic flux density increases, the iron loss becomes larger than in the case of a uniform magnetic flux density distribution. From the viewpoint of saturation magnetization, the larger the saturation magnetization, the more the nonlinear increase in iron loss can be suppressed, so the increase in iron loss can be suppressed. Saturation magnetization is mainly determined by the amount of Si in electrical steel sheets, but it is the magnetic flux density B8 of the iron core material that is effective in increasing iron loss in the practical exciting magnetic flux density range. The results of experimentally investigating the effect of the magnetic flux density B8 of the iron core material on the iron loss of the unicore are shown. A single-phase unicore of the shape shown in FIG. 3 was produced from 0.23 mm thick grain-oriented electrical steel sheets with different magnetic flux densities B8 shown in Table 3. 50 turns of winding were performed, no-load excitation was performed at a magnetic flux density of 1.5 T and a frequency of 60 Hz, and the iron loss was measured. The results are shown in Figure 9. In the range where the magnetic flux density B8 of the grain-oriented electrical steel sheet is 1.84 T or more and 1.91 T or less, the iron loss is reduced. It is presumed that the iron loss is reduced in the above range due to the effect of alleviating magnetic flux concentration by low B8 described above and the effect of reducing the increase in iron loss by high B8.

(5) Using grain-oriented electrical steel sheets with an iron loss deterioration rate of 1.50 or less under compressive stress.

The inside of the iron core, where magnetic flux is concentrated and iron loss increases, is a part where deformation due to processing is likely to remain. Generally, if strain remains, the magnetic domain structure of that part is disturbed, the magnetic permeability deteriorates, and the iron loss of the entire iron core deteriorates. Furthermore, even when strain removal annealing is performed after processing, twins exist in the rectangular bent portion, and like residual strain, the magnetic domain structure of that portion is disturbed, magnetic permeability deteriorates, and iron loss of the entire iron core deteriorates. In short, if the increase in iron loss due to residual strain or twinning is suppressed, the increase in iron loss can be suppressed even when the magnetic flux is concentrated inside the iron core.

As a result of searching for an iron core material that can suppress the increase in core loss due to residual strain or twinning, it was found that the core loss in the transformer iron core can be reduced by selecting a material with an iron loss deterioration rate of 1.50 or less under compressive stress.

The following shows the experimental results that served as the basis for the appropriate range. A single-phase unicore of the shape shown in FIG. 3 was produced from 0.23 mm thick grain-oriented electrical steel sheets A to K having different core loss degradation rates under compressive stress shown in Table 4. Materials with different core loss deterioration rates under compressive stress (grain-oriented electrical steel sheets A to K) were produced by changing the film tension of the insulating film formed on the surface of the electrical steel sheet. As the film tension increased, the core loss degradation rate under compressive stress decreased. 50 turns of winding were performed on the fabricated unicore, no-load excitation was performed at a magnetic flux density of 1.5 T and a frequency of 60 Hz, and the iron loss was measured. Figure 10 shows the relationship between the core loss deterioration rate under compressive stress of the grain-oriented electrical steel sheet as a material and the transformer core loss. In the region where the iron loss degradation rate under compressive stress is 1.50 or less, the transformer iron loss becomes small.

Deterioration of core loss due to disturbance of the magnetic domain due to compressive stress and increase in core loss due to residual strain or twinning within the iron core are correlated, and by selecting the core material based on the core loss deterioration rate under compressive stress, the inner core of the iron core Even when the magnetic flux is concentrated, it is estimated that the increase in iron loss can be suppressed.

The present invention was made based on the above findings and has the following structure.

[1] A rolled iron core made of grain-oriented electrical steel,

The coiled iron core has a flat portion and a corner portion adjacent to the flat portion, has a wrap portion on the flat portion, has a bent portion at the corner portion, and has a ratio of the outer peripheral length to the inner peripheral length when the coiled iron core is viewed from the side. (outer circumference length/inner circumference length) is 1.80 or less,

The grain-oriented electrical steel sheet has a magnetic flux density B8 of 1.84 T or more and 1.91 T or less when the magnetic field intensity H is 800 A/m, and an iron loss deterioration rate under compressive stress calculated by the following formula. A rolled iron core that is 1.50 or less.

Core loss deterioration rate under compressive stress = (core loss at 5 MPa compressive stress)/(core loss in the absence of compressive stress)

Here, the iron loss at a compressive stress of 5 MPa and the iron loss in the absence of compressive stress in the above equation are the iron loss (W/kg) measured under the conditions of a frequency of 50 Hz and a maximum magnetization of 1.7 T, respectively, and the compressive stress The iron loss at 5 MPa is the iron loss measured at a compressive stress of 5 MPa in the rolling direction of the grain-oriented electrical steel sheet.

[2] The iron core according to [1], wherein the grain-oriented electrical steel sheet has been subjected to heat-resistant magnetic domain refining treatment.

[3] A method of manufacturing a rolled iron core made of a grain-oriented electrical steel sheet, having a flat portion and a corner portion adjacent to the flat portion, a wrap portion on the flat portion, and a bent portion on the corner portion, comprising:

The ratio of the length of the outer circumference to the length of the inner circumference of the iron core when viewed from the side (length of the outer circumference/length of the inner circumference) is 1.80 or less,

As the above-mentioned grain-oriented electrical steel sheet, the magnetic flux density B8 when the magnetic field intensity H is 800 A/m is 1.84 T or more and 1.91 T or less, and the core loss degradation rate under compressive stress calculated by the following formula is 1.50 or less. The manufacturing method of the rolled iron core used.

Core loss deterioration rate under compressive stress = (core loss at 5 MPa compressive stress)/(core loss in the absence of compressive stress)

Here, the iron loss at a compressive stress of 5 MPa and the iron loss in the absence of compressive stress in the above equation are the iron loss (W/kg) measured under the conditions of a frequency of 50 Hz and a maximum magnetization of 1.7 T, respectively, and the compressive stress The iron loss at 5 MPa is the iron loss measured at a compressive stress of 5 MPa in the rolling direction of the grain-oriented electrical steel sheet.

[4] The method for producing a rolled iron core according to [3], wherein the grain-oriented electrical steel sheet is subjected to heat-resistant magnetic domain refining treatment.

According to the present invention, a winding iron core with excellent magnetic properties and low transformer iron loss and a method for manufacturing the same can be provided. According to the present invention, a rolled iron core with excellent magnetic properties and small transformer core loss can be obtained without using two or more types of materials with different magnetic properties (core loss).

According to the present invention, the complexity of iron core design, such as the arrangement of materials required when two or more types of materials with different magnetic properties are used, is reduced, and a rolled iron core with excellent magnetic properties with small core loss can be obtained with high manufacturability. .

Figure 1 is a schematic diagram explaining the magnetic path inside the iron core and the magnetic path outside the iron core of a wound iron core.
FIG. 2 is a schematic diagram explaining the movement of magnetic flux in the direction perpendicular to the steel plate in a steel plate joint.
Figure 3 is an explanatory diagram (side view) explaining the shapes of the experimentally produced tranco core and uni core.
Fig. 4 is an explanatory diagram explaining the arrangement of the search coil when examining the magnetic flux density distribution in the iron core.
Fig. 5 is a diagram showing the results of an investigation into the concentration of magnetic flux in the iron cores of tranco cores and uni cores.
FIG. 6 is a diagram showing the results of investigating the influence of the magnetic flux density B8 of the iron core material on the magnetic flux concentration in the iron core of the unicore.
Figure 7 is an explanatory diagram (side view) explaining the shape of an experimentally manufactured iron core.
Figure 8 is a diagram showing the relationship between the ratio of the length of the outer circumference to the length of the inner circumference in each iron core shape and the concentration of magnetic flux inside the iron core.
Figure 9 is a diagram showing the results of investigating the influence of the magnetic flux density B8 of the iron core material on the iron loss of the unicore.
Figure 10 is a diagram showing the relationship between the iron loss deterioration rate and the transformer iron loss under compressive stress of the iron core material.
Fig. 11 is an explanatory view (side view) explaining the shape of the tranco core manufactured in the example.
Fig. 12 is an explanatory view (side view) explaining the shape of the uni-core manufactured in the example.

Below, the details of the present invention are explained.

<Kwon Cheol-sim>

As described above, in order to achieve a transformer core with low core loss, it is necessary to satisfy the following conditions.

(A) A coiled iron core having a flat portion and a corner portion adjacent to the flat portion, a wrap portion on the flat portion, and a bent portion on the corner portion.

(B) The ratio of the length of the outer circumference of the iron core to the length of the inner circumference is 1.80 or less.

(A) is satisfied by selecting a manufacturing method for the iron core, generally called uni-core or duo-core type. The manufacturing method of the rolled iron core can be a known method. More specifically, when using a Unicore manufacturing machine manufactured by AEM, when the design size is read by the manufacturing machine, the steel sheet is produced one by one with the steel sheet sheared and bent at the size according to the design drawing, and the processing is completed. The rolled iron core can be manufactured by laminating steel plates.

In the condition (B), the length of the outer circumference and inner circumference of the iron core refer to the length of the outer circumference and the inner circumference of the iron core, respectively, when the iron core is viewed from the side. In other words, when the iron core is viewed from the side, the length of the outer circumference of the iron core is measured along the outer side (outer surface) of the grain-oriented electrical steel sheet (material) constituting the rolled iron core. is the length of one turn in the winding direction, and the length of the inner circumference of the iron core is along the inner side (inner surface) of the grain-oriented electrical steel sheet located innermost among the grain-oriented electrical steel sheets constituting the winding iron core in the winding direction of the grain-oriented electrical steel sheet. It is 1 turn long. The upper limit of the ratio of the length of the outer circumference of the iron core to the length of the inner circumference needs to be 1.80. The ratio is preferably 1.70 or less, and more preferably 1.60 or less. The lower limit of the ratio is not specifically specified in terms of characteristics, but as the ratio approaches 1, the core thickness decreases, so it is determined in the relationship between the core size and thickness. As an example, the lower limit of the ratio is 1.05.

If the requirements of (A) and (B) above are controlled within the scope of the present invention, the type of steel plate joint, size of iron core, bending angle of bend, number of bends, etc. other than (A) and (B) are not particularly limited.

<Grain-oriented electrical steel sheet constituting the iron core>

As described above, in order to achieve a transformer core with low core loss, it is necessary to satisfy the following conditions.

(C) As the iron core material, use a grain-oriented electrical steel sheet with a magnetic flux density B8 of 1.84 T or more and 1.91 T or less when the magnetic field intensity H is 800 A/m.

Magnetic properties are measured by the Epstein test. The Epstein test is conducted using known methods such as IEC standards or JIS standards. Alternatively, in cases where it is difficult to evaluate the magnetic flux density B8 by the Epstein test, such as in the case of non-heat-resistant magnetic domain refinement materials, the results of the single-plate magnetic measurement test (SST) may be used instead. When conducting selection based on the suitable range of magnetic flux density B8 described above regarding the manufacture of rolled iron core, the representative characteristics of grain-oriented electrical steel coils should be used. Specifically, a test sample is taken from the stern end of the steel sheet coil, the Epstein test is performed, the magnetic flux density B8 is measured, and the average value is adopted as a representative characteristic. Alternatively, materials may be selected based on the characteristic values (average value and guaranteed value) of the steel sheet provided by the steel material manufacturer. The magnetic flux density B8 is preferably 1.86 T or more.

(D) As the iron core material, use a grain-oriented electrical steel sheet with an iron loss deterioration rate under compressive stress of 1.50 or less obtained by the formula below.

Core loss deterioration rate under compressive stress = (core loss at 5 MPa compressive stress)/(core loss in the absence of compressive stress)

The iron loss at a compressive stress of 5 MPa and the iron loss in the absence of compressive stress, defined in the formula above, are the iron loss (W/kg) measured under the conditions of a frequency of 50 Hz and a maximum magnetization of 1.7 T using the same single plate magnetic measurement device. In addition, the iron loss at the compressive stress of 5 MPa is the iron loss measured at the compressive stress of 5 MPa in the rolling direction of the grain-oriented electrical steel sheet used as the iron core material. Compressive stress is applied to the compression side at 5 MPa along one axis of the rolling direction of the steel sheet. The method of applying compressive stress is not specifically defined, but for example, there is a method of fixing one side of the steel plate with a clamp or the like and applying stress from the opposite side with a pusher or the like. In that case, it is necessary to apply stress uniformly along the rolling direction to prevent the steel sheet from buckling. Additionally, in order to prevent buckling, the steel plate may be fixed in the vertical direction up and down within a range that does not interfere with measurement. Additionally, the iron loss in the absence of compressive stress is the iron loss measured without applying compressive stress. In the present invention, as described above, a grain-oriented electrical steel sheet having an iron loss deterioration rate under compressive stress of 1.50 or less is used as the iron core material. The iron loss deterioration rate under the compressive stress is preferably 1.45 or less. Additionally, the lower limit of the iron loss deterioration rate under the compressive stress is not particularly limited, but as an example, the lower limit of the iron loss deterioration rate under the compressive stress is 1.05.

As long as the requirements of (C) and (D) above are controlled within the scope of the present invention, the characteristics, components, manufacturing methods, etc. of the grain-oriented electrical steel sheets other than (C) and (D) are not particularly limited.

Below, the components and manufacturing method of a grain-oriented electrical steel sheet suitable as a material for the winding iron core of the present invention are described.

[Ingredients Composition]

In the present invention, the component composition of the slab for grain-oriented electrical steel sheet may be any composition that allows secondary recrystallization to occur. Additionally, when using an inhibitor, for example, Al and N may be contained in appropriate amounts if an AlN-based inhibitor is used, and Mn, Se, and/or S may be contained in appropriate amounts if an MnS·MnSe-based inhibitor is used. Of course, you can use both inhibitors together. In this case, the preferred contents of Al, N, S, and Se are Al: 0.010 to 0.065 mass%, N: 0.0050 to 0.0120 mass%, S: 0.005 to 0.030 mass%, and Se: 0.005 to 0.030 mass%. .

Additionally, the present invention can be applied to grain-oriented electrical steel sheets that do not use inhibitors and have limited Al, N, S, and Se contents. In this case, the amounts of Al, N, S, and Se are preferably suppressed to 100 mass ppm or less for Al, 50 mass ppm or less for N, 50 mass ppm for S or less, and 50 mass ppm for Se.

The basic components and optionally added components of the slab for grain-oriented electrical steel are described in detail as follows.

C: 0.08 mass% or less

C is added to improve the structure of the hot rolled sheet. However, if the C content exceeds 0.08 mass%, it becomes difficult to reduce C to 50 mass ppm or less, at which self-aging does not occur during the manufacturing process. Therefore, the C content is preferably set to 0.08 mass% or less. Additionally, regarding the lower limit of the C content, there is no need to specifically set it because secondary recrystallization is possible even for materials that do not contain C. That is, the C content may be 0 mass%.

Si: 2.0 to 8.0 mass%

Si is an element effective in increasing the electrical resistance of steel and improving iron loss. When the Si content is 2.0% by mass or more, it becomes easier to obtain a sufficient iron loss reduction effect. On the other hand, if the Si content is 8.0 mass% or less, a significant decrease in workability can be suppressed, and it is also easy to suppress a decrease in magnetic flux density. Therefore, the Si content is preferably in the range of 2.0 to 8.0 mass%.

Mn: 0.005 to 1.000 mass%

Mn is an element necessary to improve hot workability. If the Mn content is 0.005% by mass or more, the effect of its addition becomes easy to obtain. On the other hand, if the Mn content is 1.000% by mass or less, it becomes easy to suppress a decrease in the magnetic flux density of the product plate. Therefore, the Mn content is preferably in the range of 0.005 to 1.000 mass%.

Cr: 0.02 to 0.20 mass%

Cr is an element that promotes the formation of a dense oxide film at the interface between the forsterite film and the base iron. Although it is possible to form an oxide film even without adding Cr, by adding 0.02% by mass or more of Cr, expansion of the preferable range of other components can be expected. Additionally, if the Cr content is 0.20% by mass or less, the oxide film can be prevented from becoming too thick, and it becomes easy to suppress deterioration of the coating peel resistance. Therefore, the Cr content is preferably in the range of 0.02 to 0.20 mass%.

It is preferable that the slab for grain-oriented electrical steel sheet contains the above-mentioned components as basic components. In addition to the above components, the slab may appropriately contain the elements described below.

Ni: 0.03 to 1.50 mass%, Sn: 0.010 to 1.500 mass%, Sb: 0.005 to 1.500 mass%, Cu: 0.02 to 0.20 mass%, P: 0.03 to 0.50 mass%, and Mo: 0.005 to 0.100 mass%. at least 1 species

Ni is a useful element for improving the structure of a hot-rolled sheet and improving its magnetic properties. If the Ni content is 0.03% by mass or more, the effect of improving magnetic properties can be more easily obtained. If the Ni content is 1.50 mass% or less, unstable secondary recrystallization can be suppressed, and the risk of deterioration of the magnetic properties of the product plate can be easily reduced. Therefore, when containing Ni, the Ni content is preferably in the range of 0.03 to 1.50 mass%.

In addition, Sn, Sb, Cu, P, and Mo are each useful elements for improving magnetic properties, and if the content of each component is more than the lower limit, the effect of improving magnetic properties can be more easily obtained. On the other hand, if the content of each of the above components is below the upper limit, it is easy to reduce the risk of inhibiting the development of secondary recrystallized grains. Therefore, when it contains Sn, Sb, Cu, P, and Mo, it is preferable that the content of each of the above elements is within the above range.

In addition, the remainder other than the above components is unavoidable impurities and Fe mixed in during the manufacturing process.

Next, a method for manufacturing a grain-oriented electrical steel sheet suitable as a material for the winding iron core of the present invention will be described.

[heating]

A slab having the above chemical composition is heated according to a conventional method. The heating temperature is preferably 1150 to 1450°C.

[Hot rolling]

After the heating, hot rolling is performed. After casting, hot rolling may be performed immediately without heating. In the case of thin cast steel, hot rolling may be performed, or hot rolling may be omitted. When performing hot rolling, it is desirable to carry out the rolling temperature of the final pass of rough rolling at 900°C or higher and the rolling temperature of the final pass of finish rolling at 700°C or higher.

[Hot rolled sheet annealing]

After that, hot-rolled sheet annealing is performed as needed. At this time, in order to develop the Goss structure to a high degree in the product sheet, the range of 800 to 1100°C is suitable as the annealing temperature for the hot rolled sheet. If the hot-rolled sheet annealing temperature is less than 800°C, the band structure from hot rolling remains, making it difficult to realize a well-defined primary recrystallization structure, and there is a risk that the development of secondary recrystallization may be inhibited. On the other hand, if the annealing temperature of the hot-rolled sheet exceeds 1100°C, the grain size after annealing of the hot-rolled sheet becomes excessively coarse, so there is a risk that it will be very difficult to realize the established primary recrystallization structure.

[Cold rolling]

After that, cold rolling is performed once or twice or more with intermediate annealing in between. The suitable intermediate annealing temperature is 800°C or higher and 1150°C or lower. Additionally, the intermediate annealing time is preferably about 10 to 100 seconds.

[Decarburization Annealing]

After that, decarburization annealing is performed. In decarburization annealing, it is preferable that the annealing temperature is 750 to 900°C, the oxidizing atmosphere PH ₂ O/PH ₂ is 0.25 to 0.60, and the annealing time is about 50 to 300 seconds.

[Application of annealing separator]

Afterwards, an annealing separator is applied. The annealing separator has MgO as its main component and is preferably applied in an application amount of about 8 to 15 g/m ² .

[Finish Annealing]

Afterwards, final annealing is performed for the purpose of secondary recrystallization and formation of a forsterite film. It is preferable that the annealing temperature is 1100°C or higher and the annealing time is 30 minutes or more.

[Planarizing treatment and insulation coating]

Afterwards, planarization treatment (flattening annealing) and insulation coating are performed. In addition, it is also possible to correct the shape by simultaneously performing a flattening treatment by applying and baking the insulating coating when applying the insulating coating. Flattening annealing is preferably performed at an annealing temperature of 750 to 950°C and an annealing time of about 10 to 200 seconds. In the present invention, an insulating coating can be applied to the surface of the steel sheet before or after planarization annealing. The insulating coating here means a coating that provides tension to the steel sheet (tension coating) to reduce core loss. Examples of tension coatings include inorganic coatings containing silica and ceramic coatings using physical vapor deposition or chemical vapor deposition methods.

In general, the core loss deterioration rate under compressive stress decreases when the tensile tension to the steel sheet due to the surface coating (forsterite coating and insulating coating) is greater. In order to increase film tension, the thickness of the tension coating can be increased, but there is concern about deterioration of the space factor. In order to obtain strong tension without worsening the space factor, in the case of inorganic coatings containing silica, there are measures such as promoting glass crystallization by raising the baking temperature. Additionally, applying a film with a low thermal expansion coefficient, such as a ceramic coating, is also effective in obtaining strong tension.

[Magnetic domain refinement processing]

In order to reduce the iron loss of the steel sheet, it is desirable to perform magnetic domain refining treatment. Magnetic domain refinement technology is a technology that reduces iron loss by subdividing the width of magnetic domains by introducing non-uniformity to the surface of a steel sheet using physical methods. Magnetic domain refinement technology can be roughly divided into heat-resistant type magnetic domain refinement, whose effectiveness is not impaired by strain relief annealing, and non-heat-resistant type magnetic domain refinement, whose effectiveness is reduced by strain relief annealing. In the present invention, it can be applied to any of steel sheets that have not been subjected to magnetic domain refining treatment, steel sheets that have been subjected to heat-resistant type magnetic domain refining treatment, and steel sheets that have been subjected to non-heat-resistant type magnetic domain refining treatment.

Among them, a steel sheet subjected to a heat-resistant magnetic domain refining treatment is more suitable than a steel sheet subjected to a non-heat-resistant magnetic domain refining treatment. Non-heat-resistant magnetic domain refining treatment generally involves irradiating a high-energy beam (laser, etc.) to a steel sheet after secondary recrystallization, introducing a high dislocation density region into the surface layer of the steel sheet through the irradiation, and forming a stress field accompanying it. This is the process of subdividing the magnetic domains. In non-heat-resistant magnetic domain refining treated materials (steel sheets subjected to non-heat-resistant magnetic domain refining treatment), when compressive stress is applied, the stress field caused by the energy beam irradiation is disturbed, the magnetic domain refining effect is reduced, and iron loss due to compressive stress occurs. The increase gets bigger. Therefore, a steel sheet that has undergone heat-resistant magnetic domain refining treatment is preferable. Regarding the method of heat-resistant magnetic domain refining treatment, known techniques such as forming linear grooves of a predetermined depth on the surface of a steel sheet can be applied.

Example

The present invention will be described in detail based on examples. The following examples show preferred examples of the present invention, and the present invention is not limited in any way by the examples. The embodiments of the present invention can be changed appropriately within the scope suitable for the purpose of the present invention, and all of them are included in the technical scope of the present invention.

[Example 1]

Single-phase tranco cores and uni-cores were manufactured using the iron core shapes shown in FIG. 11, Table 5, FIG. 12, and Table 6, and the grain-oriented electrical steel sheet as the iron core material shown in Table 7. In conditions 1 to 41, after molding, strain relief annealing was performed at 800°C for 2 hours. After annealing, the iron core was unwound from the joint, and a winding coil of 50 turns was inserted. In addition, in conditions 42 to 47, the above-described strain relief annealing was not performed and the above-described winding coil was inserted. Then, the transformer iron loss was measured under the conditions of an exciting magnetic flux density (Bm) of 1.5 T and a frequency (f) of 60 Hz. Under the same conditions, the results of the Epstein test of the iron core material (in the case of non-heat-resistant magnetic domain refinement, the results of single-plate magnetic measurement) were used as the material iron loss, and the iron loss increase rate BF in the transformer iron loss relative to the material iron loss was obtained. Additionally, in Table 5 (in the case of tranco core), the length of the inner periphery was calculated as 2(c+d)-8f×(1-π×90 (°)/360 (°)). Additionally, the length of the outer periphery was calculated as 2(a+b)-8e×(1-π×90 (°)/360 (°)). In addition, a and b were calculated as a = c + 2w and b = d + 2w, respectively. The inner and outer circumference lengths of the Unicore in Table 6 were calculated in the same manner as Table 2.

The results are shown in Table 7. In the preferred and optimal examples of the present invention, it was found that the BF was good and the transformer iron loss was small compared to the comparative example, showing very excellent transformer characteristics. In particular, in the optimal case using heat-resistant magnetic domain granular material, the transformer iron loss was particularly small.

Claims (4)

A rolled iron core made of grain-oriented electrical steel,
The above iron core is,
It has a flat portion and a corner portion adjacent to the flat portion, the flat portion has a wrap portion, and the corner portion has a bent portion, and the winding iron core has a ratio of the length of the outer circumference to the inner circumference when viewed from the side ( Outer circumference length/inner circumference length) is 1.80 or less,
The grain-oriented electrical steel sheet,
A winding iron core in which the magnetic flux density B8 when the magnetic field strength H is 800 A/m is 1.84 T or more and 1.91 T or less, and the core loss degradation rate under compressive stress calculated by the following equation is 1.50 or less.
Core loss deterioration rate under compressive stress = (core loss at 5 MPa compressive stress)/(core loss in the absence of compressive stress)
Here, the iron loss at a compressive stress of 5 MPa and the iron loss in the absence of compressive stress in the above equation are the iron loss (W/kg) measured under the conditions of a frequency of 50 Hz and a maximum magnetization of 1.7 T, respectively, and the compressive stress The iron loss at 5 MPa is the iron loss measured at a compressive stress of 5 MPa in the rolling direction of the grain-oriented electrical steel sheet. According to claim 1,
The grain-oriented electrical steel sheet is a rolled iron core that has been subjected to heat-resistant magnetic domain refinement treatment. A method of manufacturing a rolled iron core made of a grain-oriented electrical steel sheet, having a flat portion and a corner portion adjacent to the flat portion, the flat portion having a wrap portion, and the corner portion having a bent portion, comprising:
The ratio of the length of the outer circumference to the length of the inner circumference of the iron core when viewed from the side (length of the outer circumference/length of the inner circumference) is 1.80 or less,
The grain-oriented electrical steel sheet has a magnetic flux density B8 of 1.84 T or more and 1.91 T or less when the magnetic field intensity H is 800 A/m, and an iron loss degradation rate under compressive stress calculated by the following formula of 1.50 or less. The manufacturing method of the rolled iron core used.
Core loss deterioration rate under compressive stress = (core loss at 5 MPa compressive stress)/(core loss in the absence of compressive stress)
Here, the iron loss at a compressive stress of 5 MPa and the iron loss in the absence of compressive stress in the above equation are the iron loss (W/kg) measured under the conditions of a frequency of 50 Hz and a maximum magnetization of 1.7 T, respectively, and the compressive stress The iron loss at 5 MPa is the iron loss measured at a compressive stress of 5 MPa in the rolling direction of the grain-oriented electrical steel sheet. According to claim 3,
A method of manufacturing a rolled iron core, wherein the grain-oriented electrical steel sheet is subjected to heat-resistant magnetic domain refinement treatment.